Solder interconnection structure and process for making

ABSTRACT

Solder interconnection encapsulant, encapsulated structure and method for its fabrication and use, whereby the gap created by solder connections between a carrier substrate and a semiconductor device is filled with a composition obtained from curing a preparation containing a cycloaliphatic polyepoxide and/or curable cyanate ester or prepolymer thereof; filler, e.g., an aluminum nitride or aluminum oxide filler, having a maximum particle size of 31 microns.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisonal of application Ser. No. 08/059,003 filed May 6, 1993and a continuation-in-part of our commonly assigned U.S. applicationSer. No. 07/737,473, filed Jul. 30, 1991, for SOLDER INTERCONNECTIONSTRUCTURE AND PROCESS FOR MAKING, now U.S. Pat. No. 5,250,848, which wasa division of our commonly assigned U.S. application Ser. No.07/624,973, filed Dec. 10, 1990, now U.S. Pat. No. 5,089,440, issuedFeb. 18, 1992, for SOLDER INTERCONNECTION STRUCTURE AND PROCESS FORMAKING, which was a division of our commonly assigned U.S. applicationSer. No. 07/493,126, filed Mar. 14, 1990, now U.S. Pat. No. 4,999,699,issued Mar. 12, 1991, for SOLDER INTERCONNECTION STRUCTURE AND PROCESSFOR MAKING.

DESCRIPTION

1. Technical Field

The present invention is concerned with interconnection structures forjoining an integrated semiconductor device to a carrier substrate andparticularly to a structure for forming solder interconnection jointsthat exhibit improved fatigue life and stability. The present inventionis especially concerned with so-called "controlled collapse chipconnection" or "C4" that employs solder-bump interconnections. Such isalso referred to as the face down or flip-chip bonding. The presentinvention is also concerned with a flowable material for making theinterconnection structure, and with a method of making theinterconnection structure.

2. Background

Controlled collapse chip connection (C4) or flip-chip technology hasbeen successfully used for over twenty years for interconnecting highI/O (input/output) count and area array solder bumps on the siliconchips to the base ceramic chip carriers, for example alumina carriers.The solder bump, typically a lead/tin alloy such as 95 Pb/5 Sn alloy, ora lead/indium alloy, such as 50 Pb/50 In, provides the means of chipattachment to the ceramic chip carrier for subsequent usage and testing.For example, see U.S. Pat. Nos. 3,401,126 and 3,429,040 to Miller andassigned to the assignee of the present application, for a furtherdiscussion of the controlled collapse chip connection (C4) technique offace down bonding of semiconductor chips to a carrier. Typically, amalleable pad of metallic solder is formed on the semiconductor devicecontact site and solder joinable sites are formed on the conductors onthe chip carrier.

The device carrier solder joinable sites are surrounded bynon-solderable barriers so that when the solder on the semiconductordevice contact sites melts, surface tension of the molten solderprevents collapse of the joints and thus holds the semiconductor devicesuspended above the carrier. With the development of the integratedcircuit semiconductor device technology, the sizes of individual activeand passive circuit elements and gates have become very small, thenumber of circuit elements and gates in the integrated circuit hasincreased dramatically, and the integration of multiple functions on asingle chip, with increasing numbers of circuits per chip, has increasedexplosively. This results in significantly larger chip sizes with largernumbers of I/O terminals. This trend will continue and will placeincreasingly higher demands on chip joining technology. An advantage ofsolder joining a device to a substrate is that the I/O terminals can bedistributed over substantially the entire top surface of thesemiconductor device. This allows an efficient use of the entiresurface, which is more commonly known as area array bonding.

Usually the integrated circuit semiconductor devices are mounted onsupporting substrates made of materials with coefficients of thermalexpansion that differ from the coefficient of thermal expansion of thematerial of the semiconductor device, i.e. silicon. Normally the deviceis formed of monocrystalline silicon with a coefficient of thermalexpansion of 2.5×10⁻⁶ per °C. and the substrate is formed of a ceramicmaterial, typically alumina with a coefficient of thermal expansion of5.8×10⁻⁶ per °C. or an organic substrate which can be either rigid orflexible material having a coefficient of thermal expansion ranging from6×10⁻⁶ to 24.0×10⁻⁶ per °C. In operation, the active and passiveelements of the integrated semiconductor device inevitably generate heatresulting in temperature fluctuations in both the devices and thesupporting substrate since the heat is conducted through the solderbonds. The devices and the substrate thus expand and contract indifferent amounts with temperature fluctuations, due to the differentcoefficients of thermal expansion. This imposes stresses on therelatively rigid solder terminals.

The stress on the solder bonds during operation is directly proportionalto (1) the magnitude of the temperature fluctuations, (2) the distanceof an individual bond from the neutral or central point (DNP), and (3)the difference in the coefficients of thermal expansion of the materialof the semiconductor device and the substrate, and inverselyproportional to the height of the solder bond, that is the spacingbetween the device and the support substrate. The seriousness of thesituation is further compounded by the fact that as the solder terminalsbecome smaller in diameter in order to accommodate the need for greaterI/O density, the overall height decreases.

More recently, an improved solder interconnection structure withincreased fatigue life has been disclosed in U.S. Pat. No. 4,604,644 toBeckham, et al. and assigned to the assignee of the present application,disclosure of which is incorporated herein by reference. In particular,U.S. Pat. No. 4,604,644 discloses a structure for electrically joining asemiconductor device to a support substrate that has a plurality ofsolder connections where each solder connection is joined to a solderwettable pad on the device and a corresponding solder wettable pad onthe support substrate, dielectric organic material disposed between theperipheral area of the device and the facing area of the substrate,which material surrounds at least one outer row and column of solderconnections but leaves the solder connections in the central area of thedevice free of dielectric organic material.

The preferred material disclosed in U.S. Pat. No. 4,604,644 is obtainedfrom a polyimide resin available commercially and sold under thetrademark AI-10 by Amoco Corporation. AI-10 is formed by reacting adiamine such as p,p'diaminodiphenylmethane with trimellitic anhydride oracylchloride of trimellitic anhydride. The polymer is further reactedwith γ-amino propyl triethoxy silane (A1100) or β-(3,4-epoxy cyclohexyl)ethyltrimethoxy silane (A-186) from Dow Corning. The coating material isdescribed in IBM TDB September 1970 P. 825.

The dielectric material is typically applied by first mixing it with asuitable solvent and then dispensing it along the periphery of thedevice where it can be drawn in between the device and substrate bycapillary action.

Although the above techniques have been quite successful, there stillremains room for improvement in extending the fatigue life.

SUMMARY OF THE INVENTION

The present invention is concerned with enhancing the fatigue life of C4solder connections. The present invention provides an encapsulant thatexhibits excellent wetting and coverage of the C4 connections as well asthe pin heads, circuitry, or vias under the chip that are present. Infact, the present invention makes it possible to achieve completecoverage beneath the chip. The encapsulant employed pursuant to thepresent invention exhibits even and adequate flow under thesemiconductor device as contrasted to prior encapsulants that do notadequately cover the C4 connections, pin heads, circuitry, vias, orsolder masks.

In particular, the present invention is concerned with solderinterconnection for forming connections between an integratedsemiconductor chip and a carrier substrate. The solder interconnectionincludes a plurality of solder connections that extend from the carriersubstrate to electrodes on the semiconductor chip to form a gap betweenthe carrier substrate and the semiconductor device. The gap is filledwith a composition obtained from curing a curable composition containinga binder which is a polyepoxide and/or a cyanate ester or prepolymerthereof and a filler. The polyepoxide, cyanate ester and cyanate esterprepolymer employed have viscosities at normal room temperatures (25°C.) of no greater than about 5,000 centipoise. The filler has a maximumparticle size of 31 microns. The amount of binder (i.e.--epoxy and/orcyanate ester) is about 80 to about 25 percent by weight of the total ofthe binder and filler and, correspondingly, the filler is about 20 toabout 75 percent by weight of the total of the binder and filler.

In addition, the present invention is concerned with a method ofincreasing the fatigue life of solder interconnections between asemiconductor device and a supporting substrate. The method includesattaching the chip device to the substrate by a plurality of solderconnections that extend from the supporting substrate to electrodes onthe semiconductor device to form a gap between the supporting substrateand the semiconductor device. The gap is filled with the above disclosedbinder-filler composition and the composition is cured.

SUMMARY OF THE DRAWINGS

The figure is a schematic diagram of a solder interconnection pursuantto the present invention.

BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION

To facilitate understanding of the present invention, reference is madeto the figure. In the figure, numeral 1 represents a semiconductor chipjoined to the chip carrier 2 by solder bumps 3 mated to pads 4. I/O canbe in the form of pins extending and protruding from the carrier 2, witha small portion of the pins protruding from the other side of thecarrier for carrying current thereto. Alternatively, I/O can be in theform of connections passing through lead frames or bonding pads. Whenthe carrier is an organic substrate, the pins as such are not required.Instead, electrically conductive circuitry and interconnections would beprovided such as at the periphery of substrate for connection to adesired structure. The encapsulant 5 pursuant to the present inventionprovides for essentially void free encapsulation of the solderconnections thereby assuring highly reliable devices and fills the gapforming a uniform fillet around the chip as well as covering the pinheads, circuits, vias, or solder masks under the device (not shown).

The encapsulant composition of the present invention must contain abinder selected from the group of cycloaliphatic polyepoxide, cyanateester, prepolymer of cyanate ester or mixtures thereof.

The cycloaliphatic type epoxides employed in the preferred resiningredient in the invention are selected from non-glycidyl etherepoxides containing more than one 1,2-epoxy group per molecule. Theseare generally prepared by epoxidizing unsaturated aromatic hydrocarboncompounds, such as cyclo-olefins, using hydrogen peroxide or peracidssuch as peracetic acid and perbenzoic acid. The organic peracids aregenerally prepared by reacting hydrogen peroxide with either carboxylicacids, acid chlorides, or ketones, to give the compound R--COOOH. Thesematerials are well known, and reference may be made to Byrdson, J.,Plastic Materials, 1966, 471, for their synthesis and description.

Such non-glycidyl ether cycloaliphatic epoxides are characterized byhaving a ring structure wherein the epoxide group may be part of thering or attached to the ring structure. These epoxides may also containester linkages. The ester linkages are generally not near the epoxidegroup and are relatively inert to reactions.

Examples of non-glycidyl ether cycloaliphatic epoxides would include3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (containingtwo epoxide groups which are part of the ring structures, and an esterlinkage), vinylcyclohexane dioxide (containing two epoxide groups, oneof which is part of a ring structure;3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxycyclohexane carboxylate anddicyclopentadiene dioxide, having the following respective structures:##STR1##

A distinguishing feature of many of the cycloalipahtic epoxides is thelocation of the epoxy group(s) on a ring structure rather than on analiphatic side chain. Generally, the cycloaliphatic epoxidesparticularly useful in this invention will have the formula selectedfrom the group consisting of: ##STR2## where S stands for a saturatedring structure, R is selected from the group consisting of CHOCH₂,O(CH₂)_(n) CHOCH₂, and OC(CH₃)₂ CHOCH₂ radicals, where n is 1 to 5, R'is selected from the group consisting of hydrogen, methyl, ethyl,propyl, butyl, and benzyl radicals and R" is selected from the groupconsisting of CH₂ OOC and CH₂ OOC(CH₂)₄ COO radicals.

These cycloaliphatic epoxy resins may be characterized by reference totheir epoxy equivalent weight, which is defined as the weight of epoxidein grams which contains one gram equivalent of epoxy. Suitablecycloaliphatic epoxy resins have a preferred epoxy equivalent weight ofabout 50 to about 250 grams per equivalent of epoxy. They will generallyhave a viscosity between about 5 to about 900 cp at 25 degrees C.

It is essential to the success of the present invention that the epoxidehave a viscosity at 25 degrees C. of no greater than about 1000centipoise, preferably about 300 to about 600 centipoise, and mostpreferably about 300 to about 450 centipoise.

Examples of cycloaliphatic epoxides are suggested in U.S. Pat. Nos.3,207,357; 2,890,194; 2,890,197; and 4,294,746, the disclosures of whichare hereby incorporated herein by reference. Some specific examples ofsuitable cycloaliphatic epoxides are3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate having thefollowing structure: ##STR3## and available from Union Carbide under thetrade designation ERL-4221; bis(3,4-epoxycyclohexyl)adipate, having thefollowing structure: ##STR4## and available from Union Carbide under thetrade designation ERL-4299; and vinyl cyclohexane diepoxide, having thefollowing formula: ##STR5## and available from Union Carbide under thetrade designation ERL-4206.

A discussion of various cycloaliphatic epoxides can be found in thepublication entitled "Cycloaliphatic Epoxide Systems," Union Carbide,1970, the disclosure of which is hereby incorporated herein byreference. Mixtures of cycloaliphatic epoxides can be employed whendesired. The preferred cycloaliphatic epoxide employed pursuant to thepresent invention is 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (systematic name: 7-oxabicyclo (4,10) heptane-3-carboxylicacid 7-oxabicyclo (4,1) hept-3-ylmethyl ester).

Other suitable epoxy resins which can be incorporated in the presentinvention include, for example, those represented by the followingformulas, I-IV: ##STR6## wherein each A is independently a divalenthydrocarbyl group having from 1 to about 9, and preferably from 1 to 4,carbon atoms, --O--, --SO₂ --, or --CO--; each A' is independently adivalent hydrocarbyl group having from 1 to about 9, and preferably from1 to 4 carbon atoms; Q is a hydrocarbyl group having from 1 to about 10carbon atoms; Q' is hydrogen or an alkyl group having from 1 to about 4carbon atoms; each X is independently hydrogen, bromine, chlorine, or ahydrocarbyl group having from 1 to about 9 and preferably from 1 to 4carbon atoms; m has an average value of 0 to about 12, and preferablefrom about 0.03 to about 9, and most preferably from about 0.03 to about3; m' has a value from about 0.011 to about 10, and preferably fromabout 0.05 to about 6; n has a value of 0 or 1; and n' has an averagevalue from 0 to about 10, preferably from 0 to about 5, most preferablyfrom about 0.1 to about 3.

Particularly suitable epoxy resins include, for example, the diglycidylethers of resorcinol, catechol, hydroquinone, biphenol, bisphenol A,tetrabromobisphenol A, phenol-aldehyde novolac resins, alkyl substitutedphenol-aldehyde resins, bisphenol F, tetramethylbiphenol,tetramethyltetrabromophenol, tetramethyltetrabromophenol,tetrachlorobisphenol A, combinations thereof, and the like.

The cyanate esters that can be employed pursuant to the presentinvention have two or more --O--C.tbd.N groups and are curable throughcyclotrimerization.

The cyanate esters can be monomeric or less preferably polymeric,including oligomers and can be represented by those materials containingthe following group: ##STR7## wherein A represents independently asingle bond, --C(CH₃)(H)--, --SO₂ --, --O--, --C(CF₂)₂ --, --CH₂ OCH₂--, --S--, --C(═O)--, --O--C(═O)--O--, --S(═O)--, --O--P(═O)--O--,--O--P(═O)(═O)--O--, divalent alkylene radicals such as --CH₂ -- and--C(CH₃)₂ --; divalent alkylene radicals interrupted by heteroatoms inthe chain such as O, S, and N.

Each R is independently selected from the group of hydrogen, alkylcontaining 1 to 9 carbon atoms:

Each n independently is an integer of 0 to 4.

Other cyanates useful in the method, composition, and structure of theinvention can be prepared by well known methods, for example, byreacting the corresponding polyvalent phenol with a halogenated cyanate,as described in U.S. Pat. Nos. 3,553,244; 3,740,348; and 3,755,402.

The phenol reactant can be any aromatic compound containing one or morereactive hydroxyl groups. The phenolic reactant is preferably a di- ortri-polyhydroxy compound of the formula: ##STR8## in which each a and bis independently 0, 1, 2, or 3, and at least one a is not 0; n is withinthe range of 0 to about 8, preferably 0 to 3; each R is independentlyselected from non-interfering alkyl, aryl, alkaryl, heteroatomic,heterocyclic, carbonyloxy, carboxy, and the like ring substituents, suchas hydrogen, C₁₋₆ alkyl, C₁₋₆ allyl, C₁₋₆ alkoxy, halogen, maleimide,propargyl ether, glycidyl ether, and the like; and A is a polyvalentlinking moiety which can be, for example, aromatic, aliphatic,cycloaliphatic, polycyclic, and heteroatomic. Examples of linking moietyA include --O--, --SO₂ --, --CO--, --OCOO--, --S--, --C₁₋₁₂ --,dicyclopentadienyl, aralkyl, aryl, cycloaliphatic, and a direct bond.

Specific cyanate esters that can be employed in the present inventionare available and well-known and include those discussed in U.S. Pat.Nos. 4,195,132; 3,681,292; 4,740,584; 4,745,215; 4,477,629; and4,546,131; European patent application EP0147548/82; and German Offen.2611796, disclosures of which are incorporated herein by reference.

An example of a suitable polyaromatic cyanate ester containingcycloaliphatic bridging group between aromatic rings is available fromDow Chemical Company under the designation "Dow XU-71787.00L cyanate. Adiscussion of such can be found in Bogan, et al., "Unique PolyaromaticCyanate Ester for Low Dielectric Printed Circuit Boards", Sampe Journal,Vol. 24, No. 6, November/December 1988. A preferred polyfunctionalcyanate ester is Bisphenol AD dicyanate(4,4'-ethylidenebisphenoldicyanate) available from Ciba-GiegyCorporation under the trade designation AROCY L-10, hexafluoro bisphenolA dicyanate (Arocy-40S), and bisphenol M dicyanate (RTX366), having theformula ##STR9## and commercially available from Ciba-Giegy Corporation.

The compositions employed pursuant to the present invention also includea filler and especially an inorganic filler. The particle size of thefiller must not be greater than 31 microns or less, preferably about 0.7to about 31 microns, and most preferably about 0.5 to about 20 microns.This is necessary so that the composition will readily flow in the gapbetween the chip and substrate carrier. The gap is normally about 25 toabout 160 microns and preferably about 75 to about 125 microns. Thepreferred fillers have an average particle size of about 0.5 to about 20microns.

The preferred filler can be optionally treated with a coupling agent,such as γ aminopropyltriethoxysilane (A1100) orβ-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (A186), orγ-glycidylpropyltrimethoxysilane (Z6040) from Dow-Corning. An amount ofcoupling agent which is about 0.25% by weight of filler has been foundto be satisfactory. The amount can be determined by weight loss offiller treated with coupler after burning. The amount should be morethan about a few monolayers.

Other thermally conductive and electrically insulating fillers could beused for improving the thermal heat transfer from the device to thesurroundings. Such fillers include Aluminum Oxide, 92% Alumina, 96%Alumina, Aluminum Nitride, Silicon Nitride, Silicon Carbide, BerylliumOxide, Boron Nitride and Diamond powder either high pressure or PlasmaCVD. These fillers can be used in concentrations equivalent to fusedsilica and by incorporating them into suitable low viscositythermosetting resins thermally conductive C4 encapsulating media couldbe realized.

Especially preferred fillers are aluminum oxide and aluminum nitridebecause of their high thermal conductivity.

The compositions of the present invention contain about 25 to about 80%by weight and preferably about 30 to about 60% by weight of the binderand correspondingly about 20to about 75% by weight and preferably about40 to about 70% by weight of the filler. These amounts are based uponthe total amounts of binder and filler in the composition. When thebinder includes the polyepoxide, the compositions employed in thepresent invention also include a hardening or curing agent. Thepreferred hardeners for the polyepoxides are the anhydrides of organiccarboxylic acids. The hardening agent is preferably in liquid form. If asolid hardening agent is employed, such should be melted when added tothe composition. Examples of anhydrides are methyltetrahydrophthalicanhydride; hexahydrophthalic anhydride; maleic anhydride, trimelliticanhydride; pyromellitic dianhydride, tetrahydrophthalic anhydride;phthalic anhydride; norbornenedicarboxylic anhydride; nadic methylanhydride; and methylcyclohexane-1,2-dicarboxylic anhydride.

Additional anhydrides can be found, for instance, in H. Lee and K.Neville, Handbook of Epoxy Resin, McGraw Hill, 1967, Chapter 12,disclosure of which is incorporated herein by reference.

The anhydride curing agent is generally employed in amounts constitutingon an equivalent basis, about 20% to about 120% of the cycloaliphaticepoxide employed and preferably about 75% to about 100% of the epoxideequivalents.

Preferably the curing agent is employed in amounts of about 89 to about110 parts by weight per hundred parts of polyepoxy (phr).

In addition to the binder and filler, the compositions can also includea catalyst to promote the polymerization of the epoxy and/or cyanateester.

Suitable catalysts for the epoxy include amines such as the imidazoles,tertiary amine benzyldimethylamine, 1,3-tetramethyl butane diamine, tris(dimethylaminomethyl) phenol, pyridine, and triethylenediamine, andacidic catalysts, such as stannous octoate.

Suitable catalysts for the cyanate ester include Lewis acids, such asaluminum chloride, boron trifluoride, ferric chloride, titaniumchloride, and zinc chloride; salts of weak acids, such as sodiumacetate, sodium cyanide, sodium cyanate, potassium thiocyanate, sodiumbicarbonate, and sodium boronate. Preferred catalysts are metalcarboxylates and metal chelates, such as cobalt, manganese, iron, zinc,and copper acetylacetonate or octoates or naphthenates. The amount ofcatalyst when used can vary, and generally will be 0.005 to 5 weightpercent, preferably 0.05 to 0.5 weight percent based on total solidbinder weight.

Surfactants in amounts of about 0.5% to about 3% and preferably about1.2% to about 1.6% can be used to facilitate mixing the filler with theepoxy. Suitable surfactants include silanes and non-ionic type surfaceactive agents, such as Triton X-100 from Rohm and Haas Co.

Surfactants are generally prepared by the reaction of octylphenol ornonylphenol with ethylene oxide, and have the following generalstructural formulae, respectively: ##STR10## in which the C₉ alkyl groupis a mixture of branched chain isomers and x is the average number ofethylene oxide units in the ether side chain.

In the compositions that employ a cycloaliphatic epoxide, it ispreferred to also employ small amounts of a reactive modifier, i.e., aflexibilizer. The purpose of the reactive modifier is to impartdesirable mechanical properties to the cured composition, such asflexibility and thermal shock resistance. Examples of modifiers whichcan be used are fatty acids, fatty acid anhydrides, diols, polyols,polyetherdiols, and other materials having dihydroxyl groups, carboxyl,epoxy, and/or carboxylic anhydride functionality. One preferred modifieris ethylene glycol which, when employed, is present in amounts of about0.7 to about 2 phr (per hundred parts by weight of the epoxy). Ethyleneglycol is employed as a source of hydroxyls to promote the reaction ofanhydride with the epoxy.

It has been found that a preferred composition for crack-resistantencapsulants is the product of a mixture of ethylene glycol and about 5to about 30 percent, and preferably about 10 percent polyolflexibilizer. Polyol is a polyhydric alcohol containing three or morealcohol groups. The preferred polyol is one having a molecular weightbetween about 700 and 6,000. Polyether polyols are also satisfactory.

The preferred compositions of the present invention also include anorganic dye in amounts less than about 0.2% to provide contrast.Suitable dyes are nigrosine and Orasol blue GN.

The preferred compositions employed pursuant to the present inventionare substantially free (e.g.--less than 0.2% by weight) if notcompletely free from non-reactive organic solvents. Compositionsemployed pursuant to the present invention have viscosity at 25° C.(Brookfield cone & plate Spindle 51, 20 RPM or equivalent) of about3,000 to about 17,000 centipoise and preferably about 3,000 to about10,800 centipoise. The compositions are stable for at least 12 hours.The compositions can be cured at temperatures of less than about 200° C.and preferably about 130° C. to about 180° C. in about 2 to about 6hours and preferably about 4 to 5 hours. The cured compositions havecoefficient of thermal expansion of about 25 to about 40 ppm/° C., glasstransition temperature of greater than about 130° C. and preferablyabout 140° to about 190° C. The cured compositions have Shore D hardnessof greater than 85 and preferably greater than 90, modulus of elasticityat 25° C. of greater than 250,000 psi and preferably greater than750,000 psi; volume resistivity at 25° C. of greater than 10¹³ oh-cm andpreferably greater than 10¹⁴ oh-cm.

The compositions are prepared by rapidly admixing the components undervacuum usually about 5 mm Hg either using a double planetary mixer orhigh shear mixer to provide better and homogenous compositions.

The composition is applied by dispensing through nozzles under pressureof about 15 to about 90 psi and temperatures of about 25° to about 40°C. The compositions completely cover the C4 connections and pin heads.If desired, the compositions can be pregelled by heating for about 15 toabout 60 minutes, typically about 30 minutes at about 75° to about 100°C.

The compositions are then cured by heating to about 130° to about 200°C. and preferably about 130° to about 180° C. for about 2 to about 6 andpreferably about 2 to about 4 hours. The substrate employed can be anorganic, inorganic or composite in nature. The preferred substrate canbe a ceramic module or a multilayer printed circuit board, including aprinted circuit board with a conductive metal core. The preferredceramic substrates include silicon oxides and silicates such as aluminumsilicate, and aluminum oxides. High heat transfer substrates, such asaluminum nitride substrates, may also be used.

The preferred organic substrates, either rigid or flexible, as inprinted circuit boards, include conventional FR-4 epoxy and laminatesbased on high temperature resins such as high temperature epoxies,polyimides, cyanates (triazines), fluoropolymers, benzocyclobutenes,polyphenylenesulfide, polysulfones, polyetherimides, polyetherketones,polyphenylquinoxalines, polybenzoxazoles, and polyphenylbenzobisthiazoles.

The chip carrier employed can be a flexible or rigid organic, inorganic,or composite material. Substrates having thin film redistribution layersmay also be used. The preferred substrate can be a ceramic module or amultilayer printed circuit board. The preferred ceramic substratesinclude silicon oxides and silicates, such as aluminum silicate andaluminum oxides.

Exemplary fluoropolymers include perfluoroalkylenes, aspolytetrafluoroethylene, copolymers of tetrafluoroethylene andhexafluoropropylene, copolymers of tetrafluoroethylene andperfluoro-2,2-dimethyl-1,3-dioxide, polytrifluorochloroethylene,copolymers of tetrafluoroethylene with olefins as ethylene, copolymersof trifluorochloromethane with olefins as ethylene, and polymers ofperfluoroalkyl vinyl ether. Some commercially available fluoropolymersinclude polytetrafluoroethylene, tertafluoroethylene-perfluoroalkoxy,tetrafluoroethylene-ethylene, chlorotrifluoroethylene-ethylene,chlorotrifluoroethylene, andtetrafluoroethylene-perfluoro-2,2-dimethyl-1,3 dioxide.

Commercially available fluorocarbon polymers reinforced with fiber glassparticulates are available from the Rogers Corporation under the tradedesignation RO2800 and RO2500.

The polyimides that can be used as substrates in accordance with thepresent invention include unmodified polyimides, as well as modifiedpolyimides such as polyester imides, polyamide-imide-esters,polyamide-imides, polysiloxane-imides as well as other mixed polyimides.Such are well known in the prior art and need not be described in greatdetails.

Generally, the polyimides include the following recurring unit:##STR11## where n is an integer representing the number of repeatingunits to provide a molecular weight usually about 10,000 to about100,000. R is at least one tetravalent organic radical selected from thegroup consisting of: ##STR12## in which R1 is a least on divalentradical selected from the group consisting of: ##STR13## in which R1 isa divalent organic radical selected from the group consisting ofdivalent aliphatic hydrocarbon radicals having from 1 to 4 carbon atomsand carbonyl, oxy, sulfo, hexafluoroisopropylidene and sulfonylradicals, silicon, and amino radicals. Polymers containing two or moreof the R and/or R1 radicals, especially multiple series of R1 containingamido radicals can be used.

Commercially available polyimide precursors (polyamic acid) are variouspolyimide precursors from DuPont and available under the designationPyralin. These polyimide precursors come in many grades, including thoseavailable Pyralin polyimide precursors from DuPont under the furthertrade designations PI-255, PI-2545, PI-2560, PI-5878, PHI-61454, andPI-2540. Some of these are pyromellitic dianhydride-oxydianiline(PMDA-ODA) polyimide precursors.

Commercially available chemically cured polyimides are variouspolyimides from DuPont and available under the trade designation Kapton,V-Kapton, HN-Kapton, and VN-Kapton, which are all chemically curedpolyimides are generally cured with an anhydride curing agent such asacetic anhydride. Other commercially available polyimides havingrelatively lower thermal expansion are the polyimides under the Tradedesignation Upilex-R and Upilex-SGA from Ube Industries.

Typical epoxy resins include the bisphenol A type resins obtained frombisphenol A and epichlorohydrin, resinous materials obtained by theepoxidation of novolak resins produced from a phenol and an aldehydesuch as formaldehyde with epichlorohydrin, polyfunctional epoxy resinssuch as tetraglycidyldiaminodiphenyl methane and allcyclic epoxy resinssuch as bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate. The mostpreferred epoxy employed is the bisphenol A type.

The epoxy resinous compositions also can contain accelerators and curingagents as well known in the art. Examples of suitable curing agentsinclude polyamines, primary, secondary, and tertiary amines, polyamides,polysulfides, ureaphenol-formaldehyde, and acids or anhydrides thereof.In addition, suitable curing agents include Lewis acid catalysts such asBF₃ and complexes thereof.

Many of the organic substrates employed in accordance with the presentinvention contain the resin and a reinforcing fiber such as fiber-glass.Such compositions containing fibers are usually prepared by impregnatingthe fibers with, for instance, a composition of the polymer. The amountof the polymer composition is usually about 30% to about 70% by weightand preferably about 50% to about 65% by weight of the total solidscontent of the polymer composition in the fiber-glass.

In the case of epoxy compositions such can be prepared by combining withthe reinforcing fibers, and then curing to the B-stage and cutting tothe desired shape such as a sheet. When sheets are employed, thethickness is usually about 1.5 mils to about 8 mils. The curing to theB-stage is generally achieved by using temperatures of about 80° C. toabout 110° C. for about 3 minutes to about 10 minutes. If desired, thesubstrate can then be laminated onto other substrates as well as beinginterposed between the above electrically conductive patterns present inthe support layers.

The laminating can be carried out by pressing together the desiredstructure in a preheated laminating press at a predetermined pressureand temperature as, for example, about 200 psi to about 500 psi andpreferably abut 250 psi to about 300 psi at about 180° C. The time ofthe pressing operation is variable depending upon the particularmaterials employed and the pressure applied. About 1 hour is adequatefor the above conditions.

The organic substrates include the desired electrically conductivecircuitry on the top and/or bottom surfaces of the substrate and/or noninterior planes of the substrate as well known.

Next, in order to connect the electrically conductive patterns onopposing surfaces of the dielectric material, through-holes in thestructure can be made. The through-holes can be obtained by drilling orpunching operations including mechanical drilling and laser drilling andsubsequently plated. The organic substrates are generally abut 3 toabout 300 mils thick and more usually about 40 to about 100 mils thick.

The following non-limiting examples are presented to further illustratethe present invention.

EXAMPLE 1

A composition containing about 30.05 parts by weight of3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (UnionCarbide ERL-4221), about 30.02 parts by weight of hexahydrophthalicanhydride; about 0.3 parts by weight of benzyl dimethyl amine, about 0.6part by weight of ethylene glycol, about 1.90 parts by weight of TritonX-100 surfactant from Rohm & Haas was prepared and designated as mixtureA. Compositions containing various amounts of ultra high purity AluminumNitride purchased from ICD Group,. Inc., 641 Lexington Avenue, New York,N.Y. were made and cured at 130° C. for 4 hours. The resultingproperties are presented in Table I.

                  TABLE I                                                         ______________________________________                                        Weight    Weight  Viscosity   CTE    Tg                                       mixture A of AlN  (cps)       (ppm/°C.)                                                                     (°C.)                             ______________________________________                                        13.5 (A1) 1.5       675       61.2   145                                      12.0 (A2) 3.0     1,330       55.3   144                                      10.5 (A3) 4.5     3,000       52.1   150                                       9.0 (A4) 6.0     17,000      42.4   147                                       7.5 (A5) 7.5     --          40.4   139                                      ______________________________________                                    

A sample taken from composition A4 is dispensed at a temperature ofabout 30° C. in the gap of about 5 mils between a silicon chip solderedby solder bumps to 36 mm by 36 mm Al₂ O₃ substrate having pinsprotruding therefrom. The composition is cured at about 140° C. in about2 hours. The composition after being cured has a coefficient of thermalexpansion of less than 42×10-6/° C. The composition covers well thesolder connections.

EXAMPLE 2

Compositions containing various amounts, as presented in Table II, ofBisphenol AD dicyanate available from Ciba-Giegy Corporation asArocy-L10 and Aluminum Nitride available from ICD Group Inc., and about0.2 parts by weight of Zinc Octanoate (8% Zinc in mineral spirits ) areprepared. The resulting viscosities from incorporating such filler inthe liquid cyanates are shown in Table II.

                  TABLE II                                                        ______________________________________                                        Weight         Weight  Viscosity                                              of Resin       of AIN  (cps)                                                  ______________________________________                                        13.5 (B1)      1.5       123                                                  12.0 (B2)      3.0       266                                                  10.5 (B3)      4.5      2,100                                                  9.0 (B4)      6.0     14,500                                                  7.5 (B5)      7.5     19,900                                                  6.8 (B6)      8.2     --                                                     ______________________________________                                    

Composition B5 can be easily dispensed at a temperature of about 50° C.in the gap of about 5 mils between a silicon chip soldered by solderbumps to 28×28 mm Al₂ O₃ substrate having pins protruding therefrom. Thecomposition after being cured at 200° C. in about 2 hours has a glasstransition temperature of about 220° C., and a coefficient of thermalexpansion of less than 35×10-6/° C.

EXAMPLE 3

A composition containing about 13 parts by weight of3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (UnionCarbide ERL-4221), about 54 parts by weight of aluminum oxide availablefrom Atlantic Equipment Engineers, about 12 parts by weight ofmethyl-hexahydrophthalic anhydride; about 0.3 parts by weight of benzyldimethyl amine, about 0.26 part by weight of ethylene glycol, about 0.8parts by weight of Triton X-100 surfactant from Rohm & Haas and about0.03 parts by weight of Spectrasol Black CN was prepared.

The composition was dispensed at a temperature of about 30° C. in thegap of 5 mils between a silicon chip soldered by solder bumps to a 28 mmby 28 mm Al₂ O₃ substrate having pins producing therefrom. Thecomposition was cured at about 130° C in about 4 hours. The compositioncovered the pin heads and solder bumps.

While the invention has been described with respect to certain preferredembodiments and exemplifications, it is not intended to limit the scopeof the invention thereby, but solely by the claims appended hereto.

What is claimed is:
 1. A method of increasing the fatigue life of solderinterconnections between a semiconductor device and a supportingsubstrate comprising attaching said device to said substrate by aplurality of solder connections that extend from the supportingsubstrate to electrodes on said semiconductor device to form a gapbetween said supporting substrate and said semiconductor device;fillingsaid gap with a composition that contains:A. binder selected from thegroup of a cycloaliphatic epoxide, cyanate ester, prepolymer of cyanateester and mixtures thereof, said binder having a viscosity at roomtemperature of no greater than about 5,000 centipoise; B. filler chosenfrom the group consisting of aluminum oxide, aluminum nitride, siliconnitride, silicon carbide, beryllium oxide, boron nitride, and diamondpowder, said filler having a maximum particle size of 31 microns;wherein the amount of A is about 60 to about 25 percent by weight of thetotal of A and B, and correspondingly the amount of B is about 40 toabout 75 percent by weight based upon the amount of A and B; and curingsaid composition.
 2. The method of claim 1 wherein said gap is about 15to about 160 microns wide.
 3. The method of claim 1 wherein said binderis a polyepoxide selected from the group of3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate and vinylcyclohexane diepoxide.
 4. The method of claim 1 wherein said binderincludes 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane 3 carboxylate.5. The method of claim 1 wherein the viscosity of said binder at 25° C.is about 35 to about 500 centipoise.
 6. The method of claim 1 whereinsaid filler is aluminum nitride.
 7. The method of claim 1 wherein saidfiller has particle sizes of about 0.5 to about 31 micrometers.
 8. Themethod of claim 1 wherein said amount of said binder is about 25-60% byweight and said amount of said filler is correspondingly about 40-75% byweight.
 9. The method of claim 1 wherein said composition includes ananhydride of an organic carboxylic acid hardener.
 10. The method ofclaim 9 wherein said hardener includes hexahydrophthalic anhydride ormethyl hexahydrophthalic anhydride or mixtures thereof.
 11. The methodof claim 9 wherein the amount of the hardener is about 89 to about 110phr.
 12. The method of claim 9 wherein the viscosity at 25° C. of saidcomposition is about 1,500 to about 30,000 centipoise.
 13. The method ofclaim 1 wherein said composition also includes a catalyst.
 14. Themethod of claim 1 wherein said composition also includes ethylene glycolin an amount of about 0.5 to about 2 phr.
 15. The method of claim 1wherein said composition is free of unreactive organic solvents.
 16. Themethod of claim 1 wherein said composition also includes an adhesionpromoter.
 17. The method of claim 1 wherein the composition containscoupling agent.
 18. The method of claim 17 wherein the coupling agent isselected from the group consisting of γ-amino propyl triethoxy silane,β-(3,4,-epoxy cyclohexyl) ethyltrimethoxy silane, and γ-glycidoxypropyltrimethoxy silane.
 19. The method of claim 17 wherein the couplingagent is present in an amount which is about 0.25% by weight to about 2%by weight of the binder.
 20. The method of claim 1 wherein saidsubstrate is an organic, inorganic or a composite material.
 21. Themethod of claim 1 wherein said binder is a cyanate ester.
 22. The methodof claim 1 wherein said cyanate ester is chosen from the groupconsisting of 4,4'-ethylidene bisphenol dicyanate, bisphenol-Mdicyanate, bisphenol-P dicyanate, hexafluorobisphenol A dicyanate, andmixtures thereof.
 23. The method of claim 1 wherein the substrate is anorganic substrate.
 24. The method of claim 23 wherein the organicsubstrate comprises a material chosen from the group consisting of FR-4epoxy, polyimides, cyanates (triazines), fluoropolymers,benzocyclobutenes, polyphenylenesulfide, polysulfones, polyetherimides,polyetherketones, polyphenylquinoxalines, polybenzoxazoles, andpolyphenyl benzobisthiazoles.